1/2" copper pipe coming in from the meter
Typically the water service from the street to the meter should be 3/4 or the less common 5/8 inch diameter. These will provide a good flow and pressure of supply water to the house.
The outlet side of the meter may have 1/2 inch pipe though for a second level it sometimes is a good idea to have a 3/4 coming from the meter and then tap off the feeds with 1/2 inch further into the house. Ideally it would be best to run a 3/4 inch line from the meter to a manifold and from there the 1/2 inch branch lines would run off the manifold.

You may consider having a pressure gage put on the the pipe at the meter to determine what the pressure is also determining what the flow (gpm) is being supplied to the house.

Hope this helps.